A typical wireless communication system includes a number of base stations each providing coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, whether or not user operated. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller and switches and/or gateways, and the core network may provide connectivity with one or more external transport networks such as the public switched telephone network (PSTN) and/or the Internet. With this arrangement, a UE within coverage of the system could engage in air interface communication with a base station and could thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Such a system could operate in accordance with a radio access protocol, examples of which include, without limitation, Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), and BLUETOOTH. Each RAT could define its own procedures for registration of UEs, initiation of communications, handover of UEs between base station coverage areas, and other functions.
In practice, each base station coverage area could define an air interface for carrying communications between the base station and UEs, including a downlink from the base station to UEs and an uplink from UEs to the base station. In practice, the air interface could occupy a carrier, which could be frequency division duplex (FDD), having separate ranges of frequency respectively for downlink and uplink communication, or time division duplex (TDD), having a single range of frequency multiplexed over time between downlink and uplink use.
According to the radio access protocol, the air interface could then define various resources and channels for carrying communications between the base station and UEs, including various control-plane communications (e.g., operational control signaling) and user-plane communications (e.g., bearer data such as application-layer communications).
On the downlink, for instance, the air interface could define a reference channel that carries a broadcast reference signal that UEs can measure to evaluate downlink coverage quality, as well as various other downlink control channels for carrying control signaling to UEs, and the air interface could define one or more traffic channels for carrying bearer data and the like to UEs. And on the uplink, the air interface could define an access channel for carrying UE access requests to the base station as well as various other uplink control channels for carrying control signaling to the base station, and the air interface could define one or more uplink traffic channels for carrying bearer data and the like to the base station.